The present invention relates to an endoscope for medical use and, more particularly, to a bending control mechanism which is built in the endoscope.
In general, the endoscope is composed of two main portions, of which one is a control portion and the other is a flexible insertion portion connected with the control portion and is inserted in the somatic cavity. The insertion portion includes a flexible soft portion connected with the control portion, a bent-free bending portion connected with the soft portion on the tip side of it, and a hard tip distal end portion which includes an objective window (lens) and others, is connected with the tip of the bending portion.
The endoscope is provided with a bending control mechanism for controlling the bending of the bending portion. This bending control mechanism includes a bending control lever, a pulley of which the rotational motion is controlled by the control lever, and a driving wire wound round (around) the pulley, all of the above lever, pulley, and driving wire being provided inside the control portion of the endoscope. The driving wire is connected with the bending wires through a connection member and functions as a control wire for controlling the bending portion.
The above pulley includes two juxtaposed independent grooves, each capable of winding up an independent driving wire (referred to as “driving wire winding groove” hereinafter). Here, if these two driving wires are wound round these driving wire winding grooves, one each in opposite winding directions, and then, the pulley is turned in one direction, one of two driving wires extending out from the pulley is taken up or wound up while the other is paid out or wound off from the pulley. Accordingly, two control wires connected with driving wires are controlled such that one advances and the other retreats, thus to carry out the bending control of the bending portion.
In the endoscope, however, in order to improve the observational performance, specifically to expand the area observable by the endoscope, it is desired to make a bending angle of the bending portion as large as possible. To meet the above desirable requirement, there is needed for the driving wire to have a large wire stroke.
Because of this, in order to make the wire stroke large, there has been proposed a prior art endoscope which increases the winding diameter of the pulley, round which the driving wire is wound. However, if the winding diameter of the pulley is made large, the turning torque of the pulley becomes large, which causes such inconvenience that the bending control lever requires greater force for controlling it.
On the other hand, in order to decrease the turning torque of the pulley, there is another prior art endoscope which makes the size of the pulley smaller by shortening the winding diameter of it. In the case of such a small pulley, however, as the winding diameter of the pulley is made shorter, the bending control lever has to be turned much more in order to obtain the same bending angle as obtained by the large pulley. Because of this, controllability of the bending portion is reduced.
Furthermore, in the pulley of which the winding diameter is made smaller, the more it is tried to make the stroke of the driving wire large, the more the excess driving wire has to be wound round the driving wire winding groove, for instance 2 turns or more. Because of this, the turning torque of the pulley gradually becomes larger corresponding to the number of turns of the driving wire, whereby bending control at a uniform turning torque becoming impossible. Still further, as the overlapped driving wires caused by double or more turned driving wires interfere with each, for instance rub against one another, the durability of the driving wire is reduced.
The invention has been made in view of such problems as described above. Accordingly, an object of the invention is to provide a bending control mechanism for the endoscope with high controllability, which can improve the durability of the driving wire wound round the pulley of the bending control mechanism and also enables the bending portion to be controlled with a smaller force.